250.24 Grounding Service-Supplied A/C Systems

[mark w smith]

I have a problem. I'm not doing a very good job explaining the requirements of where the grounded service conductor is connected to a grounding electrode (Article 250.24(a)(1)). If you look at the picture on page 182 of the NEC handbook you will see the illustration of these 3 locations. What is occurring in my neck of the woods is as follows. Some of the local contractors are installing an additional bonding conductor in parallel (usually a #6 green THHN, sometimes a bare) with the grounded conductor. They secure it to the neutral lug in the meter can and run it to the neutral bus in the breaker panel. Then they run it back out either through the point of entry (conduit) or out through the wall.
The NEC identifies for us the three possible points of connections. It does not state you may only use one of these connections.
This to me violates a number of different codes, but because the code does specifically state you can't do this, I'm having a terrible time convincing them they are not installing the service correctly.
I would appreciate any advice on how to resolve this.
Thank you

 

[ryan_618]

Re: 250.24 Grounding Service-Supplied A/C Systems

Take a look at 250.24(A)(5) and you will notice that it does not permit bonding the nuetral on the load-side of the service disconnect.

The fine print notes below that article should tell you where this is permitted.

Hope this helps,

[ October 06, 2003, 09:55 AM: Message edited by: ryan_618 ]

 

[mark w smith]

Re: 250.24 Grounding Service-Supplied A/C Systems

I appreciate your reply.
I started with that section myself, but they argue that this would apply to the old branch circuits for ranges and dryers.
I'm thinking of trying a new approach to this, Article 310.4. What do you think?

 

[tom baker]

Re: 250.24 Grounding Service-Supplied A/C Systems

"They secure it to the neutral lug in the meter can and run it to the neutral bus in the breaker panel"
Is this the same neutral lug the neutral is connected to? are they installing two conductors under one lug? This would be a code violation...

You would have an easier time explaining if you you had a copy of Mike Holts Grounding and Bonding text. Call or go on line to get a copy.

 

[mark w smith]

Re: 250.24 Grounding Service-Supplied A/C Systems

Hell Tom, to answer your question, each conductor has it's own lug.

I guess what I'm looking for is someone that holds a position authority to say No they can't do this and here is why....

Showing someone a worst case example is sometime the only way to make them see what will happen if you mis-interpet the code.

 

[ryan_618]

Re: 250.24 Grounding Service-Supplied A/C Systems

Originally posted by mark w smith:
I guess what I'm looking for is someone that holds a position authority to say No they can't do this and here is why....

I believe I have already done that. I am the head electrical inspector of the city I work for (not that that means anything). 250.24(A)(5) is why. Notice that this article is not addressing branch circuits per say. It simply says YOU CANNOT DO THIS!. The fine print notes to this article point you to the applicable exceptions of this rule, and none of them apply.

As far as 310.4 goes, I think you're searching a little too hard. 310.4 is for parrallel conductors. Even if you have parralleled conductors it doesn't change the fact that you cannot bond the nuetral to ground after the first point of disconnect.

 

[don_resqcapt19]

Re: 250.24 Grounding Service-Supplied A/C Systems

Ryan,
In this case, as I understand it, there is no bonding beyond the service disconenct and in that case there is no violation of 250.24(A)(5). The bonding is at the meter and in the service panel. Bonding is premitted at every point on the line side of and within the service disconnect. I believe that 310.4 is the only section that may apply here and am not sure that it even applies. 310.4 does apply the grounded conductor but it does not apply to the GEC. Here we have a GEC in parallel with the grounded conductor.
Don

 

[al hildenbrand]

Re: 250.24 Grounding Service-Supplied A/C Systems

Mark,

I am guessing that the practice you describe is inside non metallic conduit?

In my area of Minnesota, services are installed with exterior meter sockets connected by conduit to interior service center panelboards. Most of the installations are assembled with steel conduit. The steel conduit between the meter and the service disco is a conductor that carries part of the service unbalance current. Seems remarkably like an additional conductor in a PVC conduit.

The effect, the unbalance current not being confined to the "neutral", is the same. IMO, the neutral on the line side of the service disco is a messy area handed to us by "tradition".

 

[mark w smith]

Re: 250.24 Grounding Service-Supplied A/C Systems

I need to apologize to Tom. When I wrote my last response that was supposed to say "Hello".

Tom I'm Sorry.

 

[mark w smith]

Re: 250.24 Grounding Service-Supplied A/C Systems

What a can of worms!
Because of the title of 250.24 I believe the intent is as Ryan has stated, but unfortunately the code is not specfic.
Al as far as the practices it varies. Rigid, EMT, PVC, 4 Conductor SE, I have seen it just about every way you can imagine. And your right, having metal conduit would be the same as having the second conductor.

What is the worst scenario? What danger exist if allow this to continue?

Tom (again I apologize) you are an instructor, in Mike's book does he come right out and say "no" you can't do this.

If someone knows an Electrical Engineer I would be curious to read his opinion on this topic.

 

[mark w smith]

Re: 250.24 Grounding Service-Supplied A/C Systems

Al what does EC & EE mean? As if I have to ask.

 

[Guest]

Re: 250.24 Grounding Service-Supplied A/C Systems

Not Al, but:
EE=Electrical Engineer.
EC=Electrical Contractor.

[The not Al part is because you directed your question at Al but I took the liberty of answering it].

My doctor puts , M.D., P.C. after his name. I asked his staff about it and they had no clue. Later they told me it meant Personal Corporation.

[ October 06, 2003, 11:13 PM: Message edited by: awwt ]

 

[mark w smith]

Re: 250.24 Grounding Service-Supplied A/C Systems

I sorry I called you Al, Wayne. I have been trying to read and respond in between inspections and as the day goes on I have to hurry more.

 

[al hildenbrand]

Re: 250.24 Grounding Service-Supplied A/C Systems

Thanks, Wayne C.,

I, too, have been out and back, not quite as fast as you Mark.

The multiple connections of the service grounded conductor to ground is not tidy, but an outgrowth of the multiple return paths required by the NEC. The unbalance current takes all available paths. The grounding electrode system carries part of the unbalance current. In the case of occupancies that share a common metal water service, the GEC bond thereto will result in a significant current path potentially created through the neighbors service.

The GEC carries part of the unbalance current, yet it is not a "neutral". It sure acts like a neutral.

An additional conductor between the meter socket neutral bar and the service disconnect neutral - ground bond is, in some sense, a backup neutral, and it is also a shunt to reduce the current that will flow in other higher resistance paths such as the steel conduit, or even the aluminum siding the socket is mounted to.

It is curious to me that installers would go to the extra time and material expense to include this #6 conductor, especially in metal conduit. . .and, your description leaves me with the impression that a number of different companies are doing this. Is the power company the source of the idea?

 

[mark w smith]

Re: 250.24 Grounding Service-Supplied A/C Systems

Our utility company provides us with a book of standards that they would like us to follow. The standard relating to the connection point of the GEC has three illustrations. I believe two of the three have been combined over the years to create the method they are using today.

I appreciate all of your comments. If any one has any more comments please post them.

Thank you

 

[al hildenbrand]

Re: 250.24 Grounding Service-Supplied A/C Systems

Mark,

I submit that the most meaningful conversation to effect change in your jurisdiction will occur with the PoCo engineering department. Discuss how the NEC requires bonding on the line side of the service disco, emphasizing that the service grounded conductor is, electrically, bonded to the GEC and the GES at any or all points along its length all the way to the service point, thus making the service grounded conductor and the GEC the same electrical conductor. PoCo engineering diagrams showing the additional #6 conductor do not reflect the NEC minimum, thus putting the PoCo in the position of creating a new requirement above and beyond the NEC. The PoCo is also unnecessarily penalizing its customers who have to purchase the redundant #6 conductor based on the representations presented to them by the contractor who is going along with the PoCo diagram - the contractor believing that this is part of what is required for the PoCo to connect.